1. Field of the Invention
This invention relates to digital-to-analog converters, and more specifically to a step data to snychro converter useful for driving a synchro receiver with the output data of a step data transmitter.
2. Description of the Prior Art
Step data transmitters (encoders) are electromechanical digital data output devices for transforming an angular position input into a digital electrical output, whereas synchro receivers are electromechanical analog input devices having a rotor and a plurality of stator windings for transforming electrical analog signals into rotational mechanical movement. It is to be understood that the term "synchro receiver" used herein encompasses both synchro torque receivers and synchro servo systems where torque is developed by a servo system controlled by a synchro. Since step data transmitters are digital data output devices, and since synchro receivers are analog data input devices, there is a need for a converter whenever it is desired to use step data output to position a synchro receiver. The requirement of step data-to-synchro conversion is frequently encountered in the art of shipboard navigation systems in which gyrocompasses having step data output, typically at 360x data transmission speed (1 data cycle per degree of heading), are operatively coupled to repeaters, radar equipment, and autopilots designed for synchro data input, typically at 360x data transmission speed (1 synchro revolution per degree of heading). The data conversion requirement is often further complicated when the gyrocompass of one manufacturer is operatively coupled to the synchro data input device of another manufacturer, since different manufacturers typically utilize different types of step data output and/or synchro data input.
A digital-to-synchro converter well adapted to convert ten bit binary coded information to synchro output data is disclosed in U.S. Pat. No. 3,488,653 entitled "Digital-to-Synchro Converter", and assigned to the Applicants' assignee. The above referenced converter is designed such that digitally coded information representing an unknown angle is stored in a register. A counter is continually actuated by an A.C. reference voltage. The binary state of each counter stage is countinually compared with that of the corresponding register stage. The results of the comparison are applied to a logic circuit which provides an output pulse each time that angular displacement of the A.C. reference voltage equals one of eight predetermined functions of the unknown angle. A second logic means produces two trains of rectangular pulses having duty cycles determined by the time intervals between specified pairs of pulses. The rectangular pulses are passed through filters that remove the harmonics, leaving sinusoidal waves. The sinusoidal waves are applied to a Scott T transformer which converts these waves into voltages suitable for actuating a synchro receiver.
The above described converter, however, is not designed to convert one of a plurality of different step data outputs into one of a plurality of different synchro data inputs.
Accordingly, there is a need for a step data to synchro converter which is capable of performing conversions among the various types of step data outputs and synchro data inputs. In the shipboard navigation systems art, for example, there is a particular need for such a device since it would provide for the efficient operative coupling of gyrocompasses providing step data output and synchro data input equipment manufactured by different manufacturers which heretofore have been considered incompatible without the costly design of a unique converter limited to a particular application.